This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from utility model applications entitled Wide Range Raster Control Circuit for a Display Apparatus and A Wide Range Raster Control Circuit in a Display Device earlier filed in the Korea Industrial Property Office on Dec. 26, 1997 and Jun. 29, 1998 and duly assigned Serial Nos. 97-074266 and 98-024956, respectively, by that Office.
1. Field of the Invention
The present invention relates to CRT-type display devices and, more particularly, to a raster center control circuit for a CRT-type display device, such as a monitor, which uses a linear current controller that receives a microprocessor control signal generated based on raster centering data stored in a memory device, to automatically control a horizontal center position of a raster over a wide frequency range of horizontal synchronization.
2. Description of the Related Art
As shown in FIG. 1, generally, a conventional deflection circuit for operation with a deflection yoke of a CRT-type display device typically requires raster controlling means to determine a center position of a raster with respect to a CRT screen. Horizontal raster centering is performed by controlling the current through a horizontal deflection yoke operated in accordance with a frequency of a video sync signal which, in a computer system, is supplied to the display device from a video card located in the computer""s main body.
As illustrated in FIG. 1, a typical horizontal deflection circuit includes a horizontal deflection yoke 130 to regulate a horizontal display on a CRT screen of a display device according to a horizontal driving signal generated by a horizontal drive circuit (not shown). The horizontal driving signal provides the necessary current to a base of a horizontal output transistor Q1 which generates a sawtooth wave that is transmitted across a damping diode D1, a shunt capacitor C1, and the horizontal yoke 130. In order to enable the horizontal raster centering, the horizontal deflection circuit includes current controlling means 120, with one terminal connected at a node A located between a resonance coil L1 and a resonance capacitor C3, and another terminal connected at a node B located between the horizontal deflection yoke 130 and an S-correction capacitor C2.
Current controlling means 120 establishes horizontal raster positioning by adding or subtracting an appropriate DC current level to be summed, or integrated with the current flowing in the horizontal deflection yoke 130, which is a parabolic wave signal. In this way, the proper control or centering of horizontal raster positioning is accomplished by carefully varying the level and direction of the DC current integrated with the parabolic wave signal that is present at node B. This process, known as raster biasing, results in a lateral shifting or horizontal roll of the display on the CRT screen. In a conventional horizontal summary circuit, a predetermined summing current is set through a manual selection/adjustment of components (e.g., switches and diodes) during a manufacturing stage carried out prior to the completion of product assembly, so that the setting is permanently fixed within the current controlling means 120 for a given display device.
The conventional horizontal deflection circuit described above, however, exhibits several weaknesses.
First, the need to manually select and adjust display circuitry increases assembly time, which increases the tendency for errors. In addition, manual selection of components provides for a limited degree of adjustment, and is unable to provide for very minute control, which therefore leads to minor inaccuracies in horizontal centering.
Second, the above-described current controlling means is inherently limited in the type of monitor system that is employed. That is, the current controlling means 120 is most suitable for a given horizontal frequency that is permanently fixed, and thus provides poor adaptability for a wide range of horizontal sync frequencies.
Third, in many systems incorporating the above-described conventional raster centering technique, improper raster biasing occurs at a high rate among manufactured display devices. For example, should a discrepancy exist between the size, or width, of front and back porches of a horizontal blanking signal, that is, when the sync signal is not precisely centered within a blanking pulse, improper raster biasing is likely. When an overly narrow blanking pulse is used, as is the case with some computer systems, such as Macintosh computers for example, proper raster biasing is difficult to achieve.
Accordingly, in order to overcome such drawbacks in the conventional art, it is therefore an object of the present invention to provide a raster center control circuit in which more precise raster centering is performed automatically.
It is another object of the present invention to provide a raster center control circuit which reduces product assembly costs while increasing reliability.
It is still another object of the present invention to provide a raster center control circuit in which proper raster centering can be accomplished over a wide range of horizontal sync frequencies.
It is yet still another object of the present invention to provide a raster center control circuit which achieves proper raster centering for all types of computer systems, including those employing horizontal blanking pulses having narrow porches, or poorly centered sync pulses.
The above and other objects and advantages of the present invention can be achieved by a raster center control circuit for controlling horizontal rastering of a CRT-type display device that includes a horizontal deflection circuit electrically connected to a horizontal deflection yoke of the CRT-type display device, that supplies the horizontal deflection yoke with a parabolic wave signal used to determine a horizontal center position of the horizontal raster displayed on the CRT-type display device. A memory device stores predetermined raster control values according to horizontal sync signal frequencies, and a microprocessor determines a horizontal sync signal frequency and generates a raster control signal corresponding to the predetermined raster control values stored in the memory device and the determined horizontal sync signal frequency. A linear control circuit, connected to the horizontal deflection circuit, integrates the raster control signal, generated by the microprocessor, with the parabolic wave signal supplied by the horizontal deflection circuit to the horizontal deflection yoke, to control the horizontal center position of the raster.
In the raster center control circuit of the present invention, the memory device is preferably an EEPROM and the linear control circuit is preferably an operational amplifier capable of high current output.
Objects of the invention are also achieved by a raster center control circuit for controlling a raster displayed on a display device that includes a memory device to store raster control values according to horizontal sync frequencies of a video signal, and a microprocessor to generate a raster control signal corresponding to the stored raster control values and an input frequency of a video sync signal. A raster controller outputs a current signal corresponding to the raster control signal generated by the microprocessor, to control raster centering of the display device, and the current signal from the raster controller is integrated with a parabolic wave signal supplied to the horizontal deflection yoke.